The present invention relates to an apparatus for the discharge of a mass tower filled with medium or high consistency pulp of the type used in the pulp and paper industry.
It is known in the art, to dilute medium and high consistency pulp down to a maximum consistency of about 6% before discharging it from the bottom portion of a mass tower by means of a conventional centrifugal pump. During the last decade, the use of centrifugal pumps for high consistency pulp has gained ground, and therefore, it is not surprising to find that the discharge of a mass tower has been carried out through the use of a so called MC.RTM.-pump. In the known art, an MC.RTM.-pump may be positioned at the bottom of the mass tower, and if required equipped as illustrated in European patent application 87117593 and publication 0323749 so as to ensure the flow of the pulp to the pump. However, it has been shown that it is more advantageous, in accordance with a preferred embodiment Of the invention, to arrange an MC.RTM.-pump to communicate with the wall of the mass tower, so as to pump diluted pulp therefrom. By using this kind of arrangement, pulp with at least two different consistencies can be discharged from the tower.
The above referenced pump, when arranged in communication with the mass tower, is in most cases attached to the conic wall portion thereof. However, when an MC.RTM.-pump is arranged in the above described manner, significant problems can develop. As time progresses, the output of the MC.RTM.-pump gradually decreases while the energy consumption increases. The conclusion that is reached is that the pump for some reason does not receive a sufficient amount of pulp, despite the addition of dilution water, which only offers a temporary solution to the problem.
As such, an object of the present invention and as proven during tests performed, is to eliminate the above described problems. To achieve the above objective, one end of a suction duct is positioned in a zone of moving pulp located in the interior of the tower while the other end is located in an area outside of the vessel where it is connected to a pump. The end of the duct within the vessel is disposed so as to be positioned beyond the pulp layer which thickens about the periphery of the vessel. By positioning the orifice of the suction duct in a region free from the thickened pulp layer and in a region of moving pulp, the inherent problems associated with the movement and pumping of medium to high consistency pulp from a mass tower can be obviated.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific object attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.